Research On The Utilization Of Nontraditional Bauxite Resources Including Sulfur-containing Bauxite And Fly Ash

With the high-speed development of national economy, China has become the world's biggest alumina producer and consumer. Presently, the actual output of alumina is 30 million tons per year, accounting for 36% of the world. As the domestic high-quality bauxite resources are greatly depleted, the dependence on foreign resources of alumina industry has been as high as 60%.The shortage of resources has become the bottleneck of sustainable development of alumina industry. However, there are about two billion tons of sulfur-containing bauxite that has not been effectively exploitation, so development and utilization of sulfur-containing bauxite is the main way to solve the crisis of the supply of bauxite resources and to realize the sustainable development. With explosive growth of thermal power installed capacity in recent years, the volume of discharged slag has reached 300 million tons each year. The fly ash has become one of the largest industrial waste residues, but the comprehensive recovery of fly ash is less than 30%. The stockpiling of ash fly will cause severe environmental pollution and huge potential safety problems, so it makes sense to do some comprehensive utilization research on fly ash and separate alumina or silicon from it.The major components of fly ash are Al2O3 and SiO2 and the total content of them can reach 80%. So if fly ash can be used for the extraction of alumina, we can both reduce the environmental problem and expand the source of alumina. As important components of nontraditional bauxite resources, sulfur-containing bauxite and fly ash have been paid much attention by domestic and international experts. So research on these nontraditional bauxite resources is extraordinarily meaningful.At first, the thermodynamics and behavior of the reaction between sulfur in bauxite and sodium solution in Bayer process were studied in this paper. Results slowed that the gibbs free energy of reaction decreases with the elevation of temperature between the temperature range 373-573K, and the sulfur as the form of pyrite can easily react with alkali liquor. After 10 hours reaction in pre-desilication process, there was 55.84% sulfur dissolved into the solution. In the high-pressure digestion process, reaction reached equilibrium after 2 hours. The dissolution rate of sulfur achieved 90% and the sulfur was mostly in the form of S2- in solution. When the temperature of solution was lower than 85℃, the sulfur was precipitated as a kind of dark green material, which was hydroxyl-Fe polymers (Na2[FeS2(OH)2]·2H2O)At the same time, this paper studied several different methods of the separation of aluminum-silicate from fly ash. Roasting was used to excite the activity of SiO2 and Al2O3 in fly ash. After roasting with the Na2CO3 or NaOH, the fly ash generated a new material, which was similar to nepheline. Only a small amount of SiO2 and Al2O3 were dissolved into the solution. High pressure hydro thermal process was used to deal with the fly ash. The results showed that the digesting efficiency of alumina can reach 90% and the digesting efficiency of silicon dioxide was only 10% at 260℃. Flotation research indicated that the highest A/S ratio of flotation concentrate was 1.98 by positive flotation, and 1.76 by reverse flotation. It's difficult to separate alumina and silica from fly ash by flotation.